Communication system

ABSTRACT

A communication system is presented in which a base station operates a each of a plurality of cells using a respective component carrier. When the base station decides to configure a mobile telephone to use additional cells of the plurality of cells, a access control procedure is initiated to determine for each cell whether the configuration should be allowed.

TECHNICAL FIELD

The present invention relates to mobile telecommunication networks,particularly but not exclusively networks operating according to the3^(rd) Generation Partnership Project (3GPP) standards or equivalents orderivatives thereof. The invention has particular although not exclusiverelevance to the use of carrier aggregation by base stations operatingcells as open access mode, closed access mode, or hybrid access modecells.

BACKGROUND ART

Under the 3GPP standards, a NodeB (or an eNodeB/eNB in the case of theso called ‘Long Term Evolution’ or ‘LTE’) is a base station via whichmobile devices connect to the core network. Historically, base stationscomprised ‘macro’ base stations which provide communication cells havinga relatively large geographical coverage. More recently, however, basestations having a more limited geographical coverage have also beenstandardised to provide improved coverage in geographical areas where amacro base station's coverage is known to deteriorate and/or to provideadditional services targeted at specific users or groups of users.

Specifically, for example, the 3GPP standards body has adopted astandard for so called ‘home’ or ‘femto’ base stations which provide socalled ‘femto’ cells having a relatively limited geographical coverage.Where the home base station is operating in accordance with the LTEstandards, it is sometimes referred to as a HeNB. The home base stationis also sometimes referred to as a femto cell, especially in the case ofthe so called WiMAX network. Typically, a home base station provides aradio coverage (for example, 3G/4G/WiMAX) within a limited geographicalarea, often within a building, for example in a home, a small or mediumsized enterprise, a shopping mall etc., and connects to a core networkvia a suitable public network (for example via an ADSL link to theInternet) or operator network.

Optionally, the radio coverage provided by the home base stations may besupported via a ‘home (e)NodeB gateway’ (HNB-GW) which typicallyaggregates traffic from several home base stations and handlescommunication between the home base station(s) and at least one mobilitymanagement entity (MME) in the core network. The HNB-GW is, in effect,transparent to the MME and the home base station with the HNB-GWappearing to be a mobility management entity (MME) from the perspectiveof the home base station, and to be a standard base station from theperspective of the mobility management entity (MME).

A home base station can generally be configured according to any of thefollowing access modes:

-   -   a ‘closed’ access mode in which the home base station operates a        closed subscriber group (CSG) cell to which only members of the        CSG may be provided access    -   a ‘hybrid’ access mode in which the home base station operates a        CSG cell to which members of the CSG may be provided        preferential access whilst non-members are allowed        non-preferential (non-CSG) access (for example with a different        charging structure, with a different level of service, and/or        subject to CSG members being able to successfully access the        cell during high load scenarios); and    -   an ‘open’ access mode in which the home base station operates as        a normal (non-CSG) cell to which access is provided openly.

It has also been decided, as pan of the 3GPP standardisation process,that downlink operation for system bandwidths beyond 20 MHz will bebased on the aggregation of a plurality of component carriers atdifferent frequencies (this is referred to as carrier aggregation). Suchcarrier aggregation can be used to support operation in a system bothwith and without a contiguous spectrum (for example, a non-contiguoussystem may comprise component carriers at 800 MHz, 20 GHz, and 3.5 GHz).

Carrier aggregation can be particularly beneficial in a heterogeneousnetwork (HetNet), even when the system bandwidth is contiguous, and doesnot exceed 20 MHz because multiple carriers enable interferencemanagement between different classes of cells (e.g. between a macro cellof a macro base station and femto cells operated by a home base station)and also between open access, hybrid and closed subscriber group (CSG)cells operating in the same geographical vicinity.

In accordance with carrier aggregation, therefore, a macro or home basestation can operate a first ‘primary’ cell (PCell) using a firstcomponent carrier and at least one further ‘secondary’ cell (SCell) on afurther component carrier. Further, in accordance with operation of homebase stations, a home base station can operate a PCell using a firstcomponent carrier and having a first access mode (closed, hybrid oropen) and an SCell using a second component carrier and having a secondaccess mode (closed, hybrid or open), which second access mode may bedifferent to the first access mode. A home base station can also operatea PCell having a hybrid or closed access mode with an associated firstCSG comprising a first set of members and an SCell having a hybrid orclosed access mode an associated second CSG comprising a second set ofmembers, which second set of members may be different to said first setof members.

Thus, the use of open, hybrid, and closed access mode cells, incombination with carrier aggregation, has the potential to provide anoperator of a home base station with great flexibility to operatedifferent cells for different groups of subscribers—potentially withdifferent charging policies for each cell. For example, a home basestation operator could, theoretically, set up their home base station toprovide a PCell to a relatively large CSG having a relatively largenumber of members, and an SCell to a smaller CSG, comprising a subset ofthe relatively large CSG (e.g. whose members are willing to pay apremium to have access to the additional resources of the SCell).Several other similar scenarios are, of course, possible with differentcells (primary or secondary) serving distinct or overlapping subscribergroups or with one cell serving any user (i.e. open access mode),another serving only members of a particular (CSG (i.e. closed accessmode), and/or another serving members of the (CSG preferentially (i.e.hybrid access mode) but allowing other users in when sufficientresources/quality of service are available.

However, there are still a number of technical issues with the use ofopen, hybrid, and closed access mode cells, in combination with carrieraggregation, which need to be addressed if the above flexibility is tobe fully realised. Firstly, for example, the aggregation of onecomponent carrier with one or more others to provide a PCell and one ormore SCells is based on radio conditions. Hence, a home base stationthat operates a PCell and an SCell may make a decision to initiate theconfiguration of user equipment that is connected via the PCell for useof the SCell (referred to as SCell addition) based on radio conditionalone (e.g. responsive to a measurement report from the user equipment.Thus the user equipment of a subscriber to a CSG of a closed/hybridaccess mode PCell may be configured to use a closed access mode SCellhaving a CSG to which the user is not a subscriber.

Another potential issue arises when the different cells (PCell/SCell(s))via which the user equipment is connected (or is about to be configuredto use) have different respective CSGs for which different respectivecharging structures apply. In this situation, there is currently noefficient way to determine which charging structure should takeprecedence over another, and a user is unaware of how conflicts ofcharging structure will be dealt with (e.g. will they be charged themaximum or minimum charge that applies across all the cells of theaggregated component carriers).

Yet another potential issue may arise, for example, when a home basestation operates a closed/hybrid access mode PCell having a first CSG,and a closed/hybrid access mode SCell having a second CSG, and the userequipment of a subscriber to both the first CSG and the second CSG isconnected in the PCell and the SCell. In this situation, if thesubscriber's subscription to one of the CSGs expires, whilst the otherremains valid, the component carrier (cell) configuration in thesubscriber's user equipment no longer complies with a valid CSG list andthe user equipment may continue to use resources of a CSG of which thesubscriber is no longer a member (a similar issue arises when userequipment is connected to a plurality of SCells and a CSG subscriptionexpires in respect of one of those SCells).

Moreover, when a handover is required from a source home base stationoperating primary and secondary cells having a first set of CSGs, to atarget home base station operating primary and secondary cells having adifferent set of CSGs, there are potential issues in how such a handovercan be accomplished efficiently whilst maintaining appropriate accesscontrols and membership checks.

SUMMARY

Accordingly, exemplary embodiments of the present invention aim toprovide methods and apparatus which at least partially address one ormore of the above issues.

According to one aspect of the present invention, there is providedcommunication apparatus for a cellular communication system, thecommunication apparatus comprising: means for operating a first cellusing a first component carrier and at least one further cell using afurther component carrier; means for communicating with a mobilecommunication device operating in said first cell; means for determiningthat an attempt should be made to configure said mobile communicationdevice to communicate using the at least one further cell; and means fortransmitting a message to a communication entity of said communicationsystem to initiate a procedure for checking whether configuration ofsaid mobile communication device to communicate using the at least onefurther cell should be allowed; means for receiving, from thecommunication entity, a message indicating, for each further cell,whether configuration of said mobile communication device to communicateusing that further cell should be allowed; and means for communicatingwith said mobile communication device to configure said mobilecommunication device to communicate using each further cell for which arespective indication that such configuration should be allowed has beenreceived such that said mobile communication device is configured tocommunicate using each further cell for which a respective indicationthat such configuration should be allowed has been received, and saidmobile communication device is not configured to communicate using eachfurther cell for which a respective indication that such configurationshould be allowed has not been received.

According to one aspect of the present invention, there is provided acommunication entity of a cellular communication system in whichcommunication apparatus operates each of a plurality of cells using arespective component carrier, wherein said plurality of said cellscomprises a plurality of cells for which a closed subscriber group (CSG)has been defined, the communication entity comprising: means forreceiving a message to initiate a procedure for checking whetherconfiguration of a mobile communication device to communicate using anyof said cells should be allowed, said message comprising informationidentifying the CSG for each of the plurality of cells for which aclosed subscriber group (CSG) has been defined; means for determining,for each of said cells, whether configuration of a mobile communicationdevice to communicate using said cell should be allowed; and means forgenerating and transmitting a message indicating for each of said cellswhether configuration of said mobile communication device to communicateusing that cell should be allowed.

According to one aspect of the present invention, there is providedcommunication apparatus for a cellular communication system, thecommunication apparatus comprising: means for communicating with amobile communication device; means for determining that an attemptshould be made to handover communication with said communication devicefrom said communication apparatus to target communication apparatus;means for receiving an indication that said target communicationapparatus operates a plurality of target cells each using a differentrespective component carrier, wherein said plurality of said targetcells comprises a plurality of cells for which a closed subscriber group(CSG) has been defined; means for obtaining an indication for each CSGas to whether or not said mobile communication device is a member ofsaid CSG; means for transmitting a message to a communication entity ofsaid communication system to initiate a procedure for checking whetherconfiguration of said mobile communication device to communicate usingany of said target cells should be allowed, said message comprisinginformation identifying each CSG for which a respective indication thatsaid mobile communication device is a member has been obtained; andmeans for communicating with said mobile communication device tocomplete said handover procedure for each said target cell for whichconfiguration of said mobile communication device to communicate usingthat target cell is allowable.

According to one aspect of the present invention, there is providedcommunication apparatus for a cellular communication system, thecommunication apparatus comprising: means for operating each of aplurality of cells using a respective component carrier, wherein saidplurality of said cells comprises at least one cell for which a closedsubscriber group (CSG) has been defined; means for communicating with amobile communication device operating in at least one said cell forwhich a CSG has been defined of which the mobile communication device isa member; means for obtaining an indication that CSG membership of atleast one cell in which the mobile communication device is operating hasexpired for said mobile communication device; and means for ceasing CSGbased communication with said mobile communication device in each saidcell for which said CSG membership has expired.

According to one aspect of the present invention, there is providedcommunication apparatus for a cellular communication system, thecommunication apparatus comprising: means for operating each of aplurality of cells using a respective component carrier; means forcommunicating with a mobile communication device; means for transmittinga message to a communication entity of said communication system toinitiate a procedure for checking whether configuration of said mobilecommunication device to communicate using at least one of said cellsshould be allowed; means for receiving, from the communication entity, amessage indicating, for each cell represented by the message to initiatea procedure for checking whether configuration of said mobilecommunication device to communicate using at least one of said cellsshould be allowed; and means for communicating with said mobilecommunication device to configure said mobile communication device tocommunicate using at least one cell for which a respective indicationthat such configuration should be allowed has been received.

According to one aspect of the present invention, there is provided amobile communication device of a cellular communication system in whichcommunication apparatus operates each of a plurality of cells using arespective component carrier, wherein said plurality of said cellscomprises a plurality of cells for which a closed subscriber group (CSG)has been defined, the mobile communication device comprising: means forreceiving from said communication apparatus information identifying theCSG (CSG ID) for each of said plurality of cells for which a CSG hasbeen defined; means for determining from said received informationidentifying the CSG for each said cell whether or not said mobilecommunication device is a member of said CSG; and means for generatingand transmitting a message comprising, for each CSG, informationidentifying the CSG and information indicating the membership of saidmobile communication device in said CSG.

According to one aspect of the present invention, there is provided amethod performed by communication apparatus for a cellular communicationsystem, the method comprising: operating a first cell using a firstcomponent carrier and at least one further cell using a furthercomponent carrier; communicating with a mobile communication deviceoperating in said first cell; determining that an attempt should be madeto configure said mobile communication device to communicate using theat least one further cell; and transmitting a message to a communicationentity of said communication system to initiate a procedure for checkingwhether configuration of said mobile communication device to communicateusing the at least one further cell should be allowed; receiving, fromthe communication entity, a message indicating, for each further cell,whether configuration of said mobile communication device to communicateusing that further cell should be allowed; and communicating with saidmobile communication device to configure said mobile communicationdevice to communicate using each further cell for which a respectiveindication that such configuration should be allowed has been receivedsuch that said mobile communication device is configured to communicateusing each further cell for which a respective indication that suchconfiguration should be allowed has been received, and said mobilecommunication device is not configured to communicate using each furthercell for which a respective indication that such configuration should beallowed has not been received.

According to one aspect of the present invention, there is providedmethod performed by a communication entity of a cellular communicationsystem in which communication apparatus operates each of a plurality ofcells using a respective component carrier, wherein said plurality ofsaid cells comprises a plurality of cells for which a closed subscribergroup (CSG) has been defined, the method comprising: receiving a messageto initiate a procedure for checking whether configuration of a mobilecommunication device to communicate using any of said cells should beallowed, said message comprising information identifying the CSG foreach of the plurality of cells for which a closed subscriber group (CSG)has been defined; determining, for each of said cells, whetherconfiguration of a mobile communication device to communicate using saidcell should be allowed; and generating and transmitting a messageindicating for each of said cells whether configuration of said mobilecommunication device to communicate using that cell should be allowed.

According to one aspect of the present invention, there is provided amethod performed by communication apparatus for a cellular communicationsystem, the method comprising: communicating with a mobile communicationdevice; determining that an attempt should be made to handovercommunication with said communication device from said communicationapparatus to target communication apparatus; receiving an indicationthat said target communication apparatus operates a plurality of targetcells each using a different respective component carrier, wherein saidplurality of said target cells comprises a plurality of cells for whicha closed subscriber group (CSG) has been defined; obtaining anindication for each CSG as to whether or not said mobile communicationdevice is a member of said CSG; transmitting a message to acommunication entity of said communication system to initiate aprocedure for checking whether configuration of said mobilecommunication device to communicate using any of said target cellsshould be allowed, said message comprising information identifying eachCSG for which a respective indication that said mobile communicationdevice is a member has been obtained; and communicating with said mobilecommunication device to complete said handover procedure for each saidtarget cell for which configuration of said mobile communication deviceto communicate using that target cell is allowable.

According to one aspect of the present invention, there is provided amethod performed by communication apparatus for a cellular communicationsystem, the method comprising: operating each of a plurality of cellsusing a respective component carrier, wherein said plurality of saidcells comprises at least one cell for which a closed subscriber group(CSG) has been defined; communicating with a mobile communication deviceoperating in at least one said cell for which a CSG has been defined ofwhich the mobile communication device is a member; obtaining anindication that CSG membership of at least one cell in which the mobilecommunication device is operating has expired for said mobilecommunication device; and ceasing CSG based communication with saidmobile communication device in each said cell for which said CSGmembership has expired.

According to one aspect of the present invention, there is provided amethod performed by communication apparatus for a cellular communicationsystem, the method comprising: operating each of a plurality of cellsusing a respective component carrier; communicating with a mobilecommunication device; transmitting a message to a communication entityof said communication system to initiate a procedure for checkingwhether configuration of said mobile communication device to communicateusing at least one of said cells should be allowed; receiving, from thecommunication entity, a message indicating, for each cell represented bythe message to initiate a procedure for checking whether configurationof said mobile communication device to communicate using at least one ofsaid cells should be allowed; and communicating with said mobilecommunication device to configure said mobile communication device tocommunicate using at least one cell for which a respective indicationthat such configuration should be allowed has been received.

According to one aspect of the present invention, there is provided amethod performed by a mobile communication device of a cellularcommunication system in which communication apparatus operates each of aplurality of cells using a respective component carrier, wherein saidplurality of said cells comprises a plurality of cells for which aclosed subscriber group (CSG) has been defined, the method comprising:receiving from said communication apparatus information identifying theCSG (CSG ID) for each of said plurality of cells for which a CSG hasbeen defined; determining from said received information identifying theCSG for each said cell whether or not said mobile communication deviceis a member of said CSG; and generating and transmitting a messagecomprising, for each CSG, information identifying the CSG andinformation indicating the membership of said mobile communicationdevice in said CSG.

Although for efficiency of understanding for those of skill in the art,the invention will be described in detail in the context of a 3G system(UMTS, LTE), the principles of the invention can be applied to othersystems (such as WiMAX) in which mobile devices or User Equipment (UE)communicate with one of several base stations with the correspondingelements of the system changed as required.

Aspects of the invention extend to computer program products such ascomputer readable storage media having instructions stored thereon whichare operable to program a programmable processor to carry out a methodas described in the aspects and possibilities set out above or recitedin the claims and/or to program a suitably adapted computer to providethe apparatus recited in any of the claims.

Each feature disclosed in this specification (which term includes theclaims) and/or shown in the drawings may be incorporated in theinvention independently (or in combination with) any other disclosedand/or illustrated features. In particular but without limitation thefeatures of any of the claims dependent from a particular independentclaim may be introduced into that independent claim in any combinationor individually.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described by way ofexample only with reference to the attached figures in which:

FIG. 1 schematically illustrates a mobile telecommunication system;

FIG. 2 is a block diagram of a mobile telephone forming part of thesystem shown in FIG. 1;

FIG. 3 is a block diagram of a home base station forming part of thesystem shown in FIG. 1;

FIG. 4 is a block diagram of a mobility management entity forming partof the system shown in FIG. 1;

FIG. 5 is a timing diagram indicating an access control and chargingassessment procedure for use in the system shown in FIG. 1;

FIG. 6 is a timing diagram indicating a procedure for handling dynamicexpiry of CSG membership in the system shown in FIG. 1;

FIG. 7 is a timing diagram indicating a handover procedure by whichcommunication with a mobile device is transferred between a source andtarget home base station based on communication over a first interface;

FIG. 8 is a timing diagram indicating another handover procedure bywhich communication with a mobile device is transferred between a sourceand target home base station based on communication over a secondinterface;

FIG. 9 is a timing diagram indicating another potential access controland charging assessment procedure for use in the system shown in FIG. 1.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Overview

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 in which a user of a mobile telephone 3 can communicate withother users (not shown) via a ‘home’ base station 11-1, which the usermay be permitted to access. The home base station 11-1 is coupled by apublic data network (in this example the internet 13) and, in the caseof home base station 11-1, via a home base station gateway (HNB-GW) 15,to a core telephone network 8.

In the example of FIG. 1, the home base station 11-1 is an LTE home basestation (HeNB) 11-1 which connects to the HNB-GW 15 via a suitablebroadband internet connection 13 such as an ADSL or cable connection 16and is programmed with the IP address of the HNB-GW 15 so that alluplink communications are transmitted via HNB-GW 15. Thetelecommunication 1 also comprises another home base station 11-2 whicha user may be permitted to access to communicate with other users viathe home base station 11-2, an internet connection 13, and the coretelephone network 8 without connecting to an HNB-GW 15. Each home basestation 11-1, 11-2 connects to a mobility management entity (MME) 6 anda serving gateway (SGW) 7 within the core network 8 respectively via afirst ‘S1’ logical interface (S1-MME) 16-1, 16-2 and a second ‘S1’logical interface (S1-U) 17-1, 17-2. The home base stations also connectto one another via a further ‘X2’ interface 19.

Each home base station 11-1, 11-2 shown in FIG. 1 operates a respectiveplurality of ‘femto’ cells 9-1 and 10-1 a to 10-1 z, and 9-2 and 10-2 ato 10-2 z, using a component carrier set having a respective primarycomponent carrier (PCC) 12-1, 12-2 and at least one respective secondarycomponent carrier (SCC) 14-1 a to 14-1, 14-2 a to 14-2. Each home basestation 11-1, 11-2 operates a respective primary cell (PCell) 9-1, 9-2on the PCC and at least one secondary cell (SCell) 10-1 a to 10-12, 10-2a to 10-2 z on a respective SCC 14-1 a to 14-1 z and 14-2 a to 14-2 z.As seen in FIG. 1, the power of the component carriers 12, 14 used toprovide the primary and secondary cells 9, 10 is set such that thegeographical coverage of the PCell 9 of a particular home base station11, of this example, are substantially co-incident with the geographicalcoverage of the SCell 10 of that base station. However, it will beappreciated that this need not be the case and that the PCell 9 andSCells 10 operated by a home base station 11 need not be coincident.Each cell 9, 10 has its own unique physical cell identity (PCI)associated with it in the memory of the home base station.

Each home base station 11 is also able to operate its respective Pcell 9and each SCell 10, independently, in any of any of the following accessmodes:

-   -   a ‘closed’ access mode in which the home base station 11        operates a closed subscriber group (CSG) cell to which only        members of the CSG may be provided access;    -   a ‘hybrid’ access mode in which the home base station 11        operates a CSG cell to which members of the CSG may be provided        preferential access whilst non-members are allowed        non-preferential (non-CSG) access (for example with a different        charging structure, with a different level of service, and/or        subject to CSG members being able to successfully access the        cell during high load scenarios); and    -   an ‘open’ access mode in which the home base station 11 operates        as a normal (non-CSG) cell to which access is provided openly.

Further, when a plurality of cells 9, 10 of a specific home base station11 are each operating in a closed access mode or a hybrid access mode,the CSG associated with one of those cells 9, 10 may comprise anidentical or a different group of subscribers to the CSG associated withanother of those cells 9, 10. For example, the CSGs may overlap or maycomprise a completely different group of subscribers to one another, orone CSG may comprise a subset of the subscribers in the other CSG.

Access Control and Charging Assessment

As will be described in greater detail below, the components of thetelecommunication system 1, and in particular each home base station 11,are configured to enable efficient management of the addition of anSCell 10 to the cell configuration information in the mobile telephone 3whilst ameliorating the potential conflicts arising from different PCelland SCell charging structures, or different PCell and SCell CSGmemberships. This is achieved by providing an access control/membershipverification/charging assessment procedure, as part the procedure toconfigure a mobile telephone 3 to operate using an SCell 10 with anaggregated set of component carriers. Advantageously, the accesscontrol/membership verification/charging assessment procedure providedcan also manage attempts to aggregate a plurality of cellssimultaneously without the inefficiencies associated with repeating thewhole procedure for each SCell 10 individually.

CSG Subscription Expiry

The components of the telecommunication system 1, and in particular eachhome base station 11, are also configured to enable efficient managementin the event of expiry of a CSG subscription, while a mobile telephone 3remains connected in the PCell 9 and/or SCell 10. This is achieved byproviding an effective intra home base station handover procedure bywhich CSG expiry can be notified to the serving home base station 11and, on receipt of such notification, communication can fall back(‘handover’) to those cells which the mobile telephone 3 is stillallowed to access (e.g. because they are open access or because the userof the mobile telephone 3 is a subscriber to the CSG membership expiryto the MME 6.

Handover

The components of the telecommunication system 1 are also configured toenable efficient management of handover from a source home base stationoperating primary and secondary cells having a first set of CSGs to atarget home base station operating primary and secondary cells having adifferent set of CSGs. This is achieved by providing handover proceduresin which multiple cells operated by a single home base station 11 can besubject to an access control/membership verification/charging assessmentprocedure at the same time, and the result informed to the target homebase station 11 for each cell, thereby avoiding potentially timeconsuming repeated inappropriate attempts by the target home basestation 11 to perform carrier aggregation, for example, by attempting toadd component carriers 14 on which closed access mode SCells 10 areprovided having CSGs to which the mobile telephone's user is not asubscriber.

Mobile Telephone

FIG. 2 schematically illustrates the main components of the mobiletelephone 3 shown in FIG. 1. As shown, the mobile telephone 3 includestransceiver circuitry 23 which is operable to transmit signals to and toreceive signals from the home base station 11 via one or more antennae25. As shown, the mobile telephone 3 also includes a controller 27 whichcontrols the operation of the mobile telephone 3 and which is connectedto the transceiver circuit 23 and to a loudspeaker 29, a microphone 31,a display 33, and a keypad 35. The controller 27 operates in accordancewith software instructions stored within memory 37. As shown, thesesoftware instructions include, among other things, an operating system39, a communication control module 41, a measurement module 42, and aCSG management module 43.

The communication control module 41 is operable for managingcommunication with the home base station 11 on the associated componentcarriers 12, 14. The measurement module 42 receives measurementconfiguration information from the home base station 11 for the purposesof configuring the mobile communication device 3 to make measurementsand/or acquire system information. The measurement module 42 alsoreceives associated requests to take measurements and/or to acquiresystem information for other (e.g. neighbouring) base stations. Themeasurement module 42 manages performance of the measurements andacquisition of system information, generates associated measurementreports, and transmits the generated reports to the home base station11. The CSG management module 43 maintains at least one list 45containing details of the CSGs of which the mobile telephone 3 is amember (e.g. an operator controlled ‘Allowed CSG list’ or ‘CSGWhitelist’ and/or a user controlled ‘User CSG list’). It will beappreciated that the CSG list 45 may be stored in the memory 37 of themobile telephone 3 and/or in a Universal Subscriber Identity Module(USIM) (not shown).

Home Base Station

FIG. 3 is a block diagram illustrating the main components of one of thehome base stations 11 shown in FIG. 1. As shown, the home base station11 includes transceiver circuitry 51 which is operable to transmitsignals to, and to receive signals from, the mobile telephone 3 via oneor more antennae 53, which is operable to transmit signals to and toreceive signals from the core network 8 (e.g. the MME 6 or SGW 7) via anetwork interface 55 either directly or indirectly (e.g. via the HNB-GW15) and which is operable to transmit signals to and to receive signalsfrom a base station via a base station interface 56. The operation ofthe transceiver circuitry 51 is controlled by a controller 57 inaccordance with software stored in memory 59. The software includes,among other things, an operating system 61, a communication controlmodule 63, a component carrier management module 65, a measurementmanagement module 67, and a CSG management module 69.

The communication control module 63 is operable to control communicationwith the mobile communication devices 3 on the component carriers 12,14, of the home base station's component carrier set and with otherentities in the system. The component carrier management module 65 isoperable to manage the use of the component carriers 12, 14 and, inparticular, the configuration and operation of the PCell 9 and SCells10. The component carrier management module 65 also manages theaggregation of the cells 9, 10 for a particular mobile telephone 3 asappropriate. The measurement management module 67 communicates with themobile communication device 3 to configure the mobile communicationdevice 3 to initiate measurements and/or acquire system information forother (e.g. neighbouring) base stations, and receives and processesmeasurement reports from the mobile communication device 3 comprisingthe measurement results/system information. The connection managementmodule 68 is operable to manage the connections of mobile telephones inthe PCell 9 and/or SCell(s) 10, and to broadcast system informationrelating to the cells 9, 10, to mobile telephones 3 in the vicinity. Theconnection management module 68 is configured to broadcast informationsuch as global cell identity (CGI), tracking area identity (TAI) and CSGID(s) for each cell operated by the home base station 11. The CSGmanagement module 69 is operable for configuring each cell 9, 10operated by the home base station 11 to use one of the CSG access modes(‘closed, ‘hybrid’, or ‘open’) and for setting up CSGs associated witheach cell 9, 10.

FIG. 4 shows an MME 6 having a transceiver circuit 201 coupled to a basestation interface 202, a HNB-GW interface 203 and a serving gatewayinterface 205.

A controller 207 is coupled to control the transceiver circuit 201 andis coupled to a memory comprising software including, among other thingsan operating system 211, a communications control module 219 and acontrol module 221.

The communications module 219 is operable to control communications withHNB-GWs 15 via the HNB-GW 203 interface and with base stations (home ormacro) via the base station interface 202. Communication between the MME6 and a serving gateway is conducted via the serving gateway interface205.

The control module 221 is operable to maintain an association between amobile telephone 3 and a base station, such as a home base station 11,and to update that association as the mobile device is handed over fromone home base station 11 to another home base station 11. In effect theMME 6 acts as a control-node for the network and is responsible fortracking the location of mobile devices 3 as they move within thenetwork. The control module is also operable to perform access controland membership check functions to determine whether a mobile telephone 3should be allowed to access a particular closed access mode cell orwhether it should operate as a CSG member or non-member in a hybridaccess mode cell. The control module also performs charging assessments,based on user and operator charging profiles, for determining whetheraccess by a mobile telephone to a particular cell operated by a homebase station 11 will cause a charging conflict (e.g. between differentcharging structures for different CSG groups or between the chargingstructures and a user charging profile). The charging information, CSGinformation and tracking information for performing these tasks may bestored locally in one or more databases in the memory 209, orexternally.

In the above description, the mobile telephone 3, the home base station11 and the MME 6 are described, for ease of understanding, as having anumber of discrete modules (base station/telephone registration modules,the parameter control module, and the connection/CSG managementmodules). Whilst these modules may be provided in this way for certainapplications, for example where an existing system has been modified toimplement the invention, in other applications, for example in systemsdesigned with the inventive features in mind from the outset, thesemodules may be built into the overall operating system or code and sothese modules may not be discernible as discrete entities.

Operation Access Control and Charging Assessment

FIG. 5 shows an exemplary timing diagram illustrating a typicalprocedure for access control/charging assessment employed in thetelecommunication system of FIG. 1.

As seen in FIG. 5, when the mobile telephone 3 is in a connected mode inthe PCell 9 of home base station 11 (at S1) but not an associated SCell10, the home base station makes a decision (at S2) to attempt toconfigure the mobile telephone 3 to operate within at least one SCell 10(i.e. ‘add’ one or more cells using an SCell addition procedure). In theexemplary timing diagram of FIG. 5, the home base station 11 makes thedecision to add the SCell(s) 10 without a measurement report because thePCell 9 and SCell(s) 10 of this embodiment are geographically coincident(e.g. as shown in FIG. 1) and so when the mobile telephone 3 isconnected in the PCell 9 it must also be within the coverage area of theSCell(s) 10. However, the decision to configure the mobile telephone 3to operate within the SCell(s) 10 may also be based on a measurementreport/proximity indication received from the mobile telephone 3 thatindicates that it is within the coverage area of the SCell(s) 10.

The home base station 11 determines (at 53) the access mode of eachSCell 10 from its associated PCI (e.g. whether or not the PCI is withina “PCI split.” comprising a set of PCIs that are reserved for closedaccess mode CSG cells and/or that are reserved for hybrid access modecells).

For SCell(s) 10 operating with either a closed or a hybrid access mode,the home base station 11 requests (at S4) that the mobile telephone 3reads and reports the system information (SI) for each SCell 10 (at S4)by sending a system information request comprising a list of the PCI ofeach SCell 10 for which information is to be reported. The mobiletelephone 3 responds (at S5) with a measurement report that includes,for each PCI in the list, information identifying the CSG (e.g. a CSGID) and membership information indicating the apparent subscriber statusof the mobile telephone 3 within the CSG represented by each CSG ID(e.g. based on a comparison of the CSG ID broadcast for the SCell withthe CSG IDs contained in a CSG ‘whitelist’ stored in the mobiletelephone 3). For SCell(s) 10 operating with an open access mode thehome base station 11 does not perform steps S4 or S5 because the systeminformation reading procedure is unnecessary.

For each open access cell, hybrid access cell and/or each cell having aCSG for which the measurement report indicates that the user of themobile telephone 3 is a subscriber (see 6), the home base station 11initiates (at S7) an access control/membership verification/chargingpolicy assessment procedure by sending an ‘access control’ request (e.g.a ‘CSG Access Control Request’) to the MME 6 (via the HNB-GW 15 in thecase of home base station 11-1) at S7.

The access control request includes an ‘access control list’ comprising,for each CSG for which access control is required, a CSG ID, andinformation identifying the Cell Access Mode. The access control requestalso includes a CSG Request. Type indication that indicates that therequest is for the purposes of carrier aggregation.

In response to the access control request (at S8), the MME 6 performsaccess control and/or membership verification as appropriate dependingon the access mode of the cell. The MME 6 also performs a comparison ofthe operator's charging structure for each SCell 10 and for the PCell 9via which the mobile telephone 3 is connected. If the charging structurefor the Pcell 9 and an SCell 10 is identical, then access can generallybe allowed. If, however, the charging structure for the PCell 9 and anSCell 10 is not identical, then access can only be allowed if theoperator's charging policy makes clear what charging structure willapply in the event that the mobile connects to both the SCell 10 andPCell 9 simultaneously (e.g. the maximum cost charging structure,minimum cost charging structure, a cumulative charging structure inwhich the charges of each charging structure (or a proportion thereofare added together). The MME 6 may also check a user charging profileassociated with the mobile telephone 3 to confirm whether the user ofthe mobile telephone has indicated that the charging structure that willbe applied if the SCell 10 is added is acceptable.

If the charging structure for the PCell 9 and SCell 10 is not identical,and there is no clearly defined charging policy, or if there is anyother charging conflict that cannot be resolved, then ‘access control’is deemed to have failed for the SCell 10 in question. If access controland membership verification do not fail for an SCell 10, and no chargingrelated issues arise, ‘access control’ is deemed not to have failed forthe SCell 10 in question.

The MME 6 indicates (at S9) the outcome of the access control/membershipverification/charging assessment procedure for each SCell 10 to the homebase station 11 by sending a response message (e.g. a CSG Access ControlResponse). The access control response message comprises, for each cellrepresented by the access control list in the original access controlrequest, information representing the outcome of the accesscontrol/membership verification/charging assessment procedure.

In the case of an open access mode SCell 10, the MME 6 indicates whetheror not component carrier aggregation should be allowed (e.g. in adedicated ‘CC Allowed’ information element set to ‘allowed’ not ‘notallowed’) in combination with an associated cell global identification(CGI).

In the case of a closed or hybrid access mode SCell 10, the MME 6reports the CSG ID) of the cells for which the access control/membershipverification/charging assessment procedure has been successful. In thecase of a hybrid mode SCell the MME 6 also reports the membership statusof the mobile telephone 3 for the associated CSG. Thus if accesscontrol, membership verification and/or the charging assessment failsthe MME 6 does not report the associated CSG ID. It will be appreciated,however, that an explicit indication may also be used as in the case ofthe open access SCell 10 (e.g. in a dedicated ‘CC Allowed’ informationelement).

Thus, the presence of a CSG ID for the CSG of a particular closed/hybridSCell 10, or the presence of CC Allowed set to ‘allowed’ for an openaccess mode SCell 10, indicates that carrier is aggregation isallowable.

On receipt of an indication that carrier aggregation is allowable for aparticular cell, the home base station 11 can proceed with aconventional SCell addition procedure as defined in the appropriatestandards (e.g. using an RRCConnectionReconfiguration message includingan sCellToAddModList information element comprising the appropriateSCell radio resource configuration information as referred to in 3GPP TS36.331 v 10.2.0, section 5.3.10.3b). After the mobile communicationdevice 3 has been configured for operation in the SCell 10, the macrobase station 11 activates (or subsequently deactivates) the SCell 10 inthe mobile communication device 3, when required. On receipt of anindication that access control has failed, the home base station 11 canabort the SCell addition procedure.

In the absence of an indication that carrier aggregation is allowable(e.g. the absence of a corresponding CSG ID) or on receipt of anindication that access control has failed (e.g. CC Allowed set to ‘notallowed’), the home base station 11 aborts the SCell addition procedurefor the corresponding cell.

Accordingly, when a home base station 11 that operates a PCell 9 and oneor more SCells 10, decides to initiate the configuration of a mobiletelephone 3 that is connected via the PCell 9 for use the SCell(s) 10(e.g. responsive to a measurement report from the mobile telephone 3),the mobile telephone 3 will not be configured to use any SCell 10 forwhich the user of the mobile telephone 3 is not a valid subscriber tothe CSG of that SCell 10. Further, the mobile telephone 3 will not beconfigured to use the SCell 10 if any charging policy issues (e.g.unresolved conflicts between different charging structures) will resultfrom the addition of the SCell 10.

CSG Subscription Expiry

FIG. 6 shows an exemplary timing diagram illustrating a typicalprocedure for handling dynamic expiry of CSG membership employed in thetelecommunication system of FIG. 1.

As seen in FIG. 6, when the mobile telephone 3 is operating (at 871) ina carrier aggregated set of cells comprising a PCell 9 and at least oneSCell 10, and the user's subscription to the CSG of one or more of thecells 9, 10 expires, the MME 6 sends (at S72) an indication of CSGexpiry to the home base station 11. The indication comprises the CSGID(s) of the CSG(s) for which expiry has occurred. The home base station11 responds to this indication (at S73) by initiating an effective intrahome base station handover from the cell 9, 10 to which the CSG expiryrelates to another aggregated cell 9, 10. The effective intra home basestation handover involves ceasing communication (at S73) using thecell(s) 9, 10 to which the CSG expiry relates (and continuingcommunication in any unaffected cells) and sending (at S74) anotification (e.g. a ‘CSG Leaving Notify’ message) to the MME 6 toconfirm that the affected CSG is no longer being used and that theeffective intra home base station handover to another cell 9, 10 hasoccurred. The notification comprises a list comprising the CSG 0) ofeach affected CSG.

If appropriate and necessary, the home base station 11 may seek one ormore other candidate SCells that are operated by the home base station11 to add to the SCell configuration of the mobile telephone 3 (e.g. atS75).

Further, if every cell 9, 10) in which the mobile telephone 3 isconnected has a CSG for which subscription expires, the home basestation 11 may initiate an intra home base station handover by adding atleast one other candidate SCell 10) subject to an access controlprocedure similar to the Access Control and Charging Assessmentprocedure described with reference to FIG. 5 but with the CSG AccessControl Request message the CSG Request Type indication set to indicatethat the request is for the purposes of handover.

If a cell operates using a hybrid access mode having an associated CSGof which the user of the mobile telephone 3 is a subscriber, and thesubscription to that CSG expires, the home base station 11 may returnthe mobile telephone 3 to non-CSG access to the hybrid access mode PCell9 after an appropriate access control/membership verification/chargingassessment procedure (e.g. similar to that described above) and ifappropriate given the capacity/quality of service available to non-CSGusers.

Accordingly, when a subscriber's subscription to a CSG expires while themobile telephone 3 of that subscriber is connected the home base station11 manages the connection to allow the mobile telephone 3 to continuecommunicating but without operating as part of a CSG of which thesubscriber is no longer a member.

Hanover (S1 Based)

FIG. 7 shows an exemplary timing diagram illustrating a typical S1interface based procedure for handover between two home base stations11, each operating a plurality of carrier aggregated cells, for thetelecommunication system of FIG. 1.

By way of example, a situation is considered in which handover from homebase station 11-1 as the source, to home base station 11-2 as thetarget, occurs (e.g. when the mobile telephone moves as indicated byarrow Z).

The source home base station 11-1 configures (at S81) the mobiletelephone 3 with proximity indication control. The mobile telephone 3responds (at S82) with an “entering” proximity indication, when itdetermines it may be near the cells 9-2, 10-2 of the target home basestation 11-2 and that any CSG ID(s) of one or more of the cells 9-2,10-2 is in the mobile telephone's CSG whitelist. The proximityindication includes the radio access technology (RAT) and frequency ofthe cell.

If a measurement configuration is not present for the concernedfrequency/RAT the source home base station 11-1 configures (at S83) themobile telephone 3 with relevant measurement configuration and themobile telephone 3 responds (at S84) with a measurement report includingthe PCI of each target cell 9-2, 10-2.

The source home base station 11-1 then requests (at S85) the mobiletelephone 3 to acquire system information for the cells 9-2, 10-2 of thetarget home base station 11-2 identified by the PCIs (i.e. systeminformation may be requested for a plurality of PCIs). In response, themobile telephone 3 performs (at S86) the system information acquisitionto acquire the relevant system information from the target home basestation 11-2 (e.g. including the global cell identity (CGI), trackingarea identity (TAI) and CSG ID(s) for each cell of the target). Themobile telephone 3 then sends (at S87) a measurement report to thesource home base station 11-1 including the CGI, TAI, a CSG II) and“member/non-member” indication for each cell 9-2, 10-2 operated by thetarget home base station 11-2.

The source home base station 11-1 includes (at S88) the CGI and CSG II)for each component carrier (cell) of the target home base station 11-2in a handover required message sent to the MME 6. The Cell AccessMode(s) for each component carrier of the target may also be includedwhere the target cell 9, 10 is a hybrid access mode cell.

The MME 6 performs access control/membership verification (at S89) foreach CSG cell 9-2, 10-2 based on the CSG ID(s) received for that cell9-2, 10-2 in the handover required message and the stored CSGsubscription data for the mobile telephone 3. The MME 6 also performs anassessment of the operator's charging structure for each of the targetcells 9-2, 10-2 (regardless of access mode) and, if any charging issuesarise (e.g. as described previously), handover to that cell is deemed tobe impermissible and the assessment fails for that cell. If the accesscontrol/membership verification/charging assessment procedure fails forevery CSG ID provided, the MME 6 ends the handover procedure by replyingwith the Handover Preparation Failure message.

Assuming that procedure does not fail for every target cell, the processcontinues.

The MME 6 generates a handover request message including the CSG 11D) ofeach target cell for which the access control/membershipverification/charging assessment has been successful. For each hybridcell (identified by the presence the Cell Access Mode in the handoverrequired message) the MME 6 determines the CSG Membership Status of themobile telephone 3 and includes it in the handover request message. TheMME 6 sends (at S90) the handover request message to the target homebase station 11-2. The handover request message may also include anexplicit indication whether carrier aggregation is allowed for each openaccess mode cell (e.g. using a ‘CC Allowed’ IE set to ‘allowed’ or ‘notallowed’ in a similar manner to that used for the CSG Access ControlResponse message described above).

The target home base station 11-2 verifies (S92) that the CSG IDs)received in the handover request message match the CSG II) broadcast ineach of the target cells and if such validation is successful allocatesresources appropriately. In the case of a hybrid access mode cell,access by the mobile telephone 3 may be prioritised (over non-membermobile telephones using the hybrid cells) if the CSG Membership Statusindicates that the mobile telephone 3 is a member.

The target home base station 11-2 may perform carrier aggregation forcells for which the access control/membership verification/chargingassessment procedure has been successful. The target home base station11-2 does not, however, perform carrier aggregation for those SCells 10for which a CSG ID is not present in the handover request message. Ifnone of the received CSG ID(s) correspond to a CSG ID broadcast by thetarget home base station 11-2 then handover resource allocation fails.

If a CSG Membership Status and associated CSG ID are received in thehandover request message for a hybrid access mode cell but the CSG If)does not correspond to the CSG ID broadcast by the target cell, thetarget home base station 11-2 provides access to the cell, to the mobiletelephone 3, as if it were a non-member. In this case, the target homebase station 11-2 returns, in a handover request acknowledge message,the actual CSG ID broadcast by each target cell for which this applies.

The target home base station 11-2 sends the handover request acknowledgemessage (at S94) to the MME 6 (via the HeNB GW 15 if present).

The MME 6 sends (at S95) a Handover Command message to the source homebase station 11-1. The source home base station 11-1 then transmits theHandover Command (RRC Connection Reconfiguration message includingmobility control information) to the mobile telephone 3 to complete thehandover process.

Accordingly, handover can occur efficiently without the target home basestation attempting to perform carrier aggregation inappropriately, forexample by attempting to add component carriers on which closed accessmode SCells are provided having CSGs to which the mobile telephone'suser is not a subscriber.

X2 Based Handover

An X2 based handover of a UE 3 between home base stations 11-1 and 11-2will now be described, by way of example only, with reference to thetiming diagram of FIG. 8.

As those skilled in the art will appreciate, the X2 interface is theinterface via which base stations communicate with each other. In an X2based handover the handover process is coordinated between the sourceand target base stations without overall control by the core network. X2based handover is therefore advantageous as it reduces load on the corenetwork.

As shown in FIG. 8, once a mobile telephone 3 establishes communicationwith a source home base station 11-1 the source home base station 11-1relays packet data between the mobile telephone 3 and the servinggateway of the core network 8 (via the HNB-GW 15). During communicationbetween the mobile telephone 3 and source home base station 11-1properties of the communication between the mobile telephone 3 and thehome base station 11-1 and other base stations are measured to assist incontrol of the mobile telephone's connection mobility. The home basestation 11-1 is operable to trigger the mobile telephone 3 to send ameasurement report to the home base station 11-1.

Based on the measurement report information and/or other radio resourcemanagement (RRM) information, the source hone base station 11-1 candetermine whether or not to hand the mobile telephone 3 off to a targethome base station 11-2. In the event that it is determined that themobile telephone 3 is to be handed off to a target home base station11-2, the source home base station 11-1 issues a CSG Access ControlRequest message to the MME 6 including the CSG ID) and access mode foreach cell, and access mode for each hybrid cell, operated by the targethome base station 11-2. Unlike the CSG Access Control Request messagesent for carrier aggregation purposes, however, the CSG Access ControlRequest message has the CSG Request Type indication set to indicate thatthe request is for the purposes of handover.

The MME 6 performs access control for each CSG cell based on the (CSGID(s) received in the CSG Access Control Request message and the storedCSG subscription data for the mobile telephone 3. If the access controlprocedure fails for all the CSGs, the MME 6 replies with the CSG AccessControl Failure message.

Otherwise, the MME 6 generates a CSG Access Control Response messageincluding the CSG ID of each target cell for which the accesscontrol/membership verification/charging assessment has been successful.For each hybrid cell (identified by the presence the Cell Access Mode inthe CSG Access Control Request message) the MME 6 determines the CSGMembership Status of the mobile telephone 3 and includes it in the CSGAccess Control Response message. The MME 6 sends the CSG Access ControlResponse message back to the source home base station 11-2.

The source home base station 11-1 transmits a handover request to thetarget home base station 11-2 which includes information necessary forthe target home base station 11-2 to prepare the handover, such asinformation relating to quality of service and other parameters. Thehandover request message includes the CSG ID of each target cell forwhich the access control/membership verification/charging assessment hasbeen successful and where appropriate the membership status (i.e. theCSG ID(s)/membership status included in the CSG Access ControlResponse).

The target home base station 11-2 verifies that the CSG ID(s) receivedin the handover request message match the CSG ID broadcast in each ofthe target cells and if such validation is successful and the necessaryresources can be granted by the target home base station 11-2, then thetarget configures the required resources to provide the required qualityof service etc. In the case of a hybrid access mode cell access by themobile telephone 3 may be prioritised (over non-member mobile telephonesusing the hybrid cells) if the CSG Membership Status indicates that themobile telephone 3 is a member.

The target home base station 11-2 may perform carrier aggregation forcells for which the access control/membership verification/chargingassessment procedure has been successful. The target home base station11-2 does not, however, perform carrier aggregation for those SCells 10for which a CSG ID is not present in the handover request message. Ifnone of the received CSG ID(s) correspond to a CSG ID) broadcast by thetarget home base station 11-2 then handover resource allocation fails.

If a CSG Membership Status and associated CSG ID are received in thehandover request message for a hybrid access mode cell but the CSG IDdoes not correspond to the CSG ID broadcast by the target cell, thetarget home base station 11-2 provides access to the cell, to the mobiletelephone 3, as if it were a non-member. In this case, the target homebase station 11-2 returns, in a handover request acknowledge message,the actual CSG ID broadcast by each target cell for which this applies.

Once the physical and link layer (L1 & L2) resources have beenconfigured, the target home base station 11-2 sends the handover requestacknowledgement message to the source home base station 11-1. Thehandover request acknowledgement message also includes a transparentcontainer to be sent to the mobile telephone as a radio resourcecontrol. RRC, message to perform the handover.

Once the source home base station 11-1 has received the handover requestacknowledgement, or as soon as the transmission of the handover commandis initiated in the downlink, data forwarding can be performed so thatdata received at the source home base station 11-1 is forwarded to thetarget home base station 11-2 to be relayed to the mobile telephone 3.

The procedure continues with a path switch request procedure to requestthat the downlink GTP (GPRS tunnelling protocol) tunnel is directed to aGTP tunnel endpoint at the target home base station 11-1, 11-2.Specifically, in response to a path switch request from the source homebase station 11-1, the MME 6 transmits an update bearer request or acreate session request to the serving gateway which may in turn relaythis request to a packet data network gateway.

In the example described above with reference to FIG. 8 the source andtarget home base station 11-1, 11-2 are served by the same servinggateway in the core network. In this case, as shown in FIG. 8 a modifybearer request message is sent from the MME 6 to the serving gateway 7and from the serving gateway 7 to the PDN gateway. As shown in FIG. 8these messages are acknowledged by the serving gateway 7 and by the PDNgateway.

In the example described with reference to FIG. 8 the modify bearerrequest and path switch request message contains the data indicating thesubscriber group access mode of each cell of the target base station andthe associated CSG ID(s) and CSG membership indications.

After the down link path is switched in the core network, packetsdestined for the UE 3 are sent to the target home base station 11-2 andthe resources previously reserved at the source home base station 11-1for the connection to the mobile telephone 3 can be released althoughany ongoing data forwarding may continue.

Modifications and Alternatives

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

In the above embodiments, a mobile telephone based telecommunicationssystem was described. As those skilled in the art will appreciate, thesignalling techniques described in the present application can beemployed in other communications system. Other communications nodes ordevices may include user devices such as, for example, personal digitalassistants, laptop computers, web browsers, etc.

In the embodiments described above, the mobile telephone and the homebase station each include transceiver circuitry. Typically thiscircuitry will be formed by dedicated hardware circuits. However, insome embodiments, part of the transceiver circuitry may be implementedas software run by the corresponding controller.

In the above embodiments, a number of software modules were described.As those skilled in the art will appreciate, the software modules may beprovided in compiled or un-compiled form and may be supplied to the homebase station or to the mobile telephone as a signal over a computernetwork, or on a recording medium. Further, the functionality performedby part or all of this software may be performed using one or morededicated hardware circuits. However, the use of software modules ispreferred as it facilitates the updating of the base stations, gateways,and the mobile telephones in order to update their functionalities.

It will be appreciated that the home base station 11 may determine (e.g.at $3 in FIG. 5) the access mode of the SCell 10 using a mechanism thatdoes not necessarily involve the PCI, for example from the global cellidentity (CGI) configuration or an explicit indication from anoperations administration and maintenance (OAM) system.

In the specific examples described above with reference to FIGS. 7 and 8the handover procedure is described with reference to a handover betweentwo home base stations 11 one of which is connected via a HNB-GW 15.However, the same handover procedure may be used in handovers betweentwo base stations in the following scenarios; both the base stationsinvolved in the handover are directly connected to the MME 6 in the corenetwork 8 instead of being connected via a HNB-GW 15; both the basestations involved in the handover are indirectly connected to the MME 6in the core network 8 via one or more HNB-GWs 15; and/or one or bothbase stations involved in the transfer may be a macro base station (e.gan eNodeB or the base station 5 as shown in FIG. 1) instead of a homebase station 11-1, 11-3. Further, the source base station may onlyoperate a single cell (e.g. a macro cell).

In the specific example described with reference to FIG. 8, the targetbase station (to which the communication link is transferred) informsthe MME 6 of the subscriber group access mode in which it is operating.However, in other examples the source base station may inform the MME ofthe subscriber group access mode of the target base station. In anotherembodiment the MME may only be told the identity of the target HNB andin response the MME may retrieve information on the subscriber groupaccess mode for the target HNB from a database, either within the MME orthe core network, or in one of the base stations or a base stationgateway.

In an alternative or additional embodiment, access control may beperformed when a connection to a home base station is initially set upas illustrated in FIG. 9. In this case, a modified Initial UE Message(or possibly a dedicated message) may be sent in which an access controllist comprising CSG IDs (where applicable) and possibly cell access modeare sent to the MME before any decision is made to add additional cells.This list may include every cell supported by the base station, may belimited to open access mode (and possibly hybrid access mode cells)supported by the base station and cells having a CSG of which the mobiletelephone is known to be a member, or may be limited only to cellshaving a CSG of which the mobile telephone is known to be a member.Access control/membership verification/charging assessment may then beperformed, in a similar manner to that described for FIG. 5, for eachcell supported by the home base station (as represented by the accesscontrol list). The MME returns the results of the accesscontrol/membership verification/charging assessment procedure for eachof these cells in an appropriate response message to indicate withcarrier aggregation can be allowed or not. The home base station canthen base a decision to configure the mobile telephone to use aparticular SCell on the information received from the MME, and add theSCell subject to the mobile telephone confirming that it is a member ofany closed access mode CSG.

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

Although the invention made by the present inventor has been describedbased on several preferred exemplary embodiments, it should beunderstood that this invention is not limited to the exemplaryembodiments but various modifications and changes are possible withoutdeparting f nm the spirit and scope of the invention.

This application is based upon and claims the benefit of priority fromUnited Kingdom patent application No. 1113943.3, filed on Aug. 12, 2011,the disclosure of which is incorporated herein in its entirety byreference.

1-41. (canceled)
 42. A base station for taking part in a procedure foradding a cell as a secondary cell, the base station comprising: a memorystoring instructions; and one or more processors configured to executethe instructions to: receive, as part of the procedure for adding thecell as the secondary cell, from a user equipment (UE) connected to thebase station, a measurement report which includes a Closed SubscriberGroup Identity (CSG ID), wherein the CSG ID included in the measurementreport is the CSG ID of a potential candidate cell for dual connectivityin which the UE will communicate via both a primary cell of the basestation and the secondary cell when the candidate cell has been added asthe secondary cell; request, as part of the procedure for adding thecell as the secondary cell, a Mobility Management Entity (MME) to verifya membership status of the UE for the CSG ID, wherein the requestincludes the CSG ID of the candidate cell; and receive, as part of theprocedure for adding the cell as the secondary cell, from the MME, aresponse which includes a CSG membership status information elementproviding a result of CSG membership verification performed at the MME.43. A method performed by a base station, as part of a procedure foradding a cell as a secondary cell, the method comprising: receiving, aspart of the procedure for adding the cell as the secondary cell, from auser equipment (UE) connected to the base station, a measurement reportwhich includes a Closed Subscriber Group Identity (CSG ID), wherein theCSG ID included in the measurement report is the CSG ID of a potentialcandidate cell for dual connectivity in which the UE will communicatevia both a primary cell of the base station and the secondary cell, whenthe candidate cell has been added as the secondary cell; requesting, aspart of the procedure for adding the cell as the secondary cell, aMobility Management Entity (MME) to verify a membership status of the UEfor the CSG ID, wherein the request includes the CSG ID of the candidatecell; and receiving, as part of the procedure for adding the cell as thesecondary cell, from the MME, a response which includes a CSG membershipstatus information element providing a result of CSG membershipverification performed at the MME.
 44. A user equipment (UE) for takingpart in a procedure for adding a cell as a secondary cell, the UEcomprising: a memory storing instructions; and one or more processorsconfigured to execute the instructions to: detect, as part of theprocedure for adding the cell as the secondary cell and when the UE isconnected to a base station, a potential candidate cell for dualconnectivity in which the UE will communicate via both a primary cell ofthe base station and the secondary cell when the candidate cell has beenadded as the secondary cell; read system information in the candidatecell, the system information comprising a Closed Subscriber GroupIdentity (CSG ID); and transmitting, to the base station, a measurementreport which includes the CSG ID.
 45. A method, performed by a userequipment (UE), as part of a procedure for adding a cell as a secondarycell, the method comprising: detecting, as part of the procedure foradding the cell as the secondary cell and when the UE is connected to abase station, a potential candidate cell for dual connectivity in whichthe UE will communicate via both a primary cell of the base station andthe secondary cell when the candidate cell has been added as thesecondary cell; reading system information in the candidate cell, thesystem information comprising a Closed Subscriber Group Identity (CSGID); and transmitting, to the base station, a measurement report whichincludes the CSG ID.